The Romanesque-Gothic Sanctuary, that today welcomes the visitor on top of the mountain, was built and modified over several centuries. There are three styles of architecture: the first is Romanesque, found in the apse, which is oriented toward the exact spot where the sun rises on the day of the Feast of St. Michael (September 29th), and in the first arch and related windows and columns; the second style is transitional Romanesque in the next two arches with piers and pointed arches; and the third style is Gothic of the school of Piacenza as seen in the decoration of the big window of the central apse and in the two windows of the side aisles.
The beginning of the construction of the church is difficult to date, but it is assumed that the project was commissioned by Abbot Stephen (1148-1170).
Originally the church was to be topped by cross vaults similar to the current ones. These vaults collapsed and, in the seventeenth century, they were replaced in the central nave by a heavy barrel vault, which exerted a considerable pressure on the side walls, threatening their stability and creating the danger of collapse. In order to face up this threat, during the restoration of the late nineteenth century, the barrel vault was demolished and replaced with a triple cross vault that was completed in 1937.
Inside the church there are majestic pillars, a multitude of minor columns, pilasters, corners … all crowned with intriguing, symbolic capitals: they number 139 in all.
The first pillar to the left of the nave is particularly interesting, as beneath it can be seen the top 15 centimetres of Mount Pirchiriano: “summit steeped in holiness,” as it was called by the Rosminian poet Clemente Rebora.
The three apses are characterized by their covering of red bricks; the two large niches at the sides of the central apse have their own Romanesque window, and over them, a Greek cross is deeply embedded into the wall.
The figures of the Major Prophets (Isaiah, Jeremiah, Ezekiel, Daniel) are found in the ample frame of the great apsidal window, whilst the base is occupied by the scene of the Annunciation of the Archangel Gabriel to Mary: the comportment and face of Mary exude a serene mysticism, which captures the attention. Four half-columns surmounted by the figures of the four evangelists with their symbols (from right, Matthew, Mark, Luke, John) are on either side of the great window. It is worth a pause at this point to contemplate the profound religious message of this sermon in stone.
A room with an irregular plan called the “Old Choir” opens out at the end of the central nave of the church. It is what remains of the church of Ugone, a place where images from of the end of the 15th Century and early 16th are abundant.
Today, it contains ten of the sixteen stone sarcophagi entombing the bodies of the princes of the Royal House of Savoy, brought from the Cathedral of Turin on 25 October 1836, when King Carlo Alberto entrusted them to the custodianship of the Rosminian religious, together with the whole abbey.
THE ORIGINAL SANCTUARY OF SAINT MICHAEL
This is made up of three small apsidal chapels, accessed from the central nave near the pillar on the right, descending 12 very ancient and well worn steps, which evoke memories of the thousands of pilgrims who have trodden them since the Middle Ages.
The hypotheses about the origin of the primitive sanctuary are numerous; they are irrevocably intertwined, as any authoritative sources are vague. However, scholars agree in identifying here the first Sacra and the original historical instance of the veneration of St. Michael. The largest chapel, having a part of the living rock at its rear, is an extension of the other two, and is now dedicated to St. John Vincent. We are in the most holy place of the Sacra.
DEFENDENTE FERRARI’S TRIPTYCH (about 1520)
This is the most precious masterpiece owned by the Sacra. The triptych was taken from the main altar, restored and placed in the Old Choir.
A delicate Madonna who breastfeeds Baby Jesus dominates the centre. She is standing on a crescent moon, in a gold mandorla, surrounded by 12 cherubs. The side panels represents St. Michael the Archangel defeating the devil, and St. John Vincent presenting to the Virgin the patron of the work, Urban of Miolans, commendatory abbot of the Sacra from 1503 to 1522. The charm of the Baby is wonderful and the position of the little feet is very natural; the beautiful face of Mary inspires confidence, her look is unassuming, the overall impression is of sweet melancholy, innocence and modesty. An exquisite dais, on which the author has painted the Visitation of Mary, the Nativity of Jesus and the Adoration of the Magi, is found at the base.
THE GREAT FRESCO OF THE ASSUMPTION (1505)
This is the largest fresco preserved in the Sacra. It was painted in 1505, on the left wall upon entering the church. It is a work of great size (measuring 6.5×4 m) mostly executed by Secondo del Bosco di Poirino, but certainly involving the hand of one of his pupils. The painter was able to divide the space harmoniously into three scenes: the Burial of Jesus, the Dormition of Mary (a rather rare subject), and Our Lady of the Assumption. The best scene is that showing Jesus lowered into the sepulchre, which captures the depth of sorrow in Mary’s face and centres one’s attention on Christ by the positioning of all the figures. The freshness of the colours is quite striking.
THE FRESCO OF THE LEGENDS (late 1600?)
This is located on the right wall of the Old Choir; it is painted in red and white on a yellowish background and summarizes the history of the foundation of the Sanctuary interspersed with legend.
Top right, St. John Vincent cuts the beams to build a little church to St. Michael on Mount Caprasio; but angels and doves carry the beams from Mount Caprasio to the top of Pirchiriano; on the upper left is the monastery of Saint Michael already built, enveloped by three tongues of flame to signify the angelic apparition; in the center, the bishop of Turin, Amizone, comes up from Avigliana and finds the church already consecrated by the Angels; in the lower left, the procession of Hugh of Montboisser progresses from Susa to the Pirchiriano in order to found the Monastery.
THE DEPOSITION OF JESUS FROM THE CROSS AND THE PREACHING OF THE DEAD (1505-1510)
The deposition of Jesus is depicted high up on the pillar of the Old Choir: this subject takes its inspiration from the scene of Jesus’ burial in the great fresco.
Beneath it is the curious scene of two skeletons speaking to a group of believers through two scrolls, one in Latin, which calls for compassion for the dead, and one in archaic French, which exhorts the living to pray for the dead and to remember their common mortal destiny.